The present invention relates to a hydraulic control system for an automatic transmission of a vehicle.
Conventional automatic transmissions used in vehicles typically include a torque converter, a powertrain realized through a multi-stage gearshift mechanism that is connected to the torque converter, and a hydraulic control system that selectively operates one of a plurality of operational elements of the powertrain based on the driving state of the vehicle.
In designing such an automatic transmission, a design concept and plan are formulated based on a variety of factors such as performance, durability, reliability, mass-producibility, and manufacturing costs. After selecting a design concept, development is pursued in three broad areas that include mechanical operation, hydraulic control (by a hydraulic control system), and electronic control.
Although the powertrain and the hydraulic control system are structured differently depending on the manufacturer, most automatic transmissions used in small and medium-sized vehicles include two planetary gearsets to provide four forward speeds and one reverse speed. Also, such automatic transmissions generally include four clutches, two brakes, two one-way clutches, and a hydraulic control system that corresponds to such a configuration. However, the application of these elements, that is, the four clutches, two brakes, and two one-way clutches complicates the structure, increases the overall size and weight of the automatic transmission, and also increases costs.
Embodiments of the present invention provide a hydraulic control system for an automatic transmission, in which four forward speeds and one reverse speed are effected while reducing the number of friction elements. This simplifies the overall structure and decreases the weight of the automatic transmission. This also reduces the cost of production of the automatic transmission.
In one embodiment, the present invention provides a hydraulic control system for an automatic transmission, in which hydraulic pressure generated in an oil pump is controlled to a predetermined level by a regulator valve. Part of this pressure is supplied as operational pressure of a damper clutch and to a reducing valve. Another part of this pressure is supplied to a hydraulic pressure control section for the selective supply of operational pressure to friction elements that are engaged in each shift range and speed. The hydraulic pressure control section including a shift control assembly, a hydraulic pressure control assembly, a switching assembly, a fail-safe assembly, and an N-R control assembly.
The shifting control assembly includes a manual valve, which is indexed with a driver-manipulated select lever to realize line conversion. The hydraulic pressure control assembly includes a first pressure control valve and a first solenoid valve controlling N-D range pressure for supply to a friction element(s) operating in third and fourth speeds, a second pressure control valve and a second solenoid valve controlling D range pressure for supply to a friction element(s) operating in second and fourth speeds, and a third pressure control valve and a third solenoid valve controlling D range pressure for control to a friction element(s) operating in first, second, and third speeds.
The switching assembly includes a switch valve effecting port conversion by line pressure supplied to both ends thereof and by hydraulic pressure supplied to the fourth solenoid valve. The switch valve also selectively supplies hydraulic pressure supplied to the first pressure control valve to a friction element(s) operating as a fixing element(s) in neutral N, park P, and reverse R ranges, and to a friction element(s) operating as an input element(s) in third and fourth speeds.
The fail-safe assembly includes a first fail-safe valve controlled by line pressure, operational pressure of a friction element(s) operating as an input element(s) in third and fourth speeds, and operational pressure of a friction element(s) operating as a fixed element(s) in second and fourth speeds. The first fail-safe valve selectively supplies hydraulic pressure supplied to the switch valve and reverse pressure supplied from the manual valve to a friction element(s) operating as a fixed element(s) in the neutral N, park P, and reverse R ranges. It also includes a second fail-safe valve controlled by N-D range pressure, R range pressure, operational pressure of a friction element(s) operating as an input element(s) in first, second, and third speeds, and operational pressure of a friction element(s) operating as an input element(s) in third and fourth speeds. The second fail-safe valve also selectively supplies control pressure of the second pressure control valve to a friction element(s) operating as a fixed element(s) in second and fourth speeds.
The N-R control valve includes an N-R control valve controlled by control pressure supplied from the second solenoid valve in the reverse R range, and supplying hydraulic pressure supplied from the manual valve to a friction element(s) operating as an input element(s) in the reverse R range.